IMO Having the fire ring hanging out allows a hot spot out that could lead to failure, maybe detonation and then failure, but really I am worried about seal and heat transfer.
Having the fire ring supported allows heat transfer to block and head, so the relatively thin ring doesn't hold all the heat.
Flush after crush wouldn't bother me, in fact, I think it would be good if it has full contact on both sides. The problem is, that these chambers tend to be larger than 4.08, so you have to match the head, not the cylinder bore
So if I understand your question "If it does have full contact on both sides, can it hang over?" I don't really like it, but depending on how far it hangs over, it should wick the heat away. Another issue there is we chase every bit of airflow, and you are now adding a lip along the cylinder wall below the valve, I wouldn't want that either.
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 445 cid FE, headers, RPM intake, 1000 HP series Holley, 4 speed